void main(){
  var count = 10;
  var conut2 = 20;

  const Safe_Top_Height = 30; // 常量
  // const Safe_Bottom_Height = count + conut2;  //编译时编译
  // 常量必须在编译时就能确定值，不能使用变量进行初始化
  final Safe_Bottom_Height1 = count + conut2; //运行时编译

  var num = count + conut2;
  // print(num); // ignore: avoid_print
  print(Safe_Bottom_Height1 + Safe_Top_Height); // ignore: avoid_print
  print(Safe_Bottom_Height1);
}